1. Field of the Invention
The present invention relates to a variable regeneration valve of a heavy equipment, and more particularly to, a variable regeneration valve of a heavy equipment in which hunting due to repeated motion of a spool does not occur in a regeneration valve that supplies a return flow of an actuator to a supply port during single operation of the actuator or its composite operation such as composite driving of arm in and swing, and a structure of the variable regeneration valve is simplified to improve process characteristics.
2. Description of the Related Art
Generally, regeneration means that a desirable operational speed of an actuator is ensured and cavitation due to shortage of flow is prevented from occurring in a supply side of the actuator by supplying the flow generated in a return side of the actuator to the supply side.
Such regeneration is based on an actuator that can be operated by its load not flow. For example, in case of an excavator, a return flow of high pressure obtained by load of a boom when the boom descends is used when the boom ascends.
FIG. 1 illustrates the state that a spool of an arm control valve is switched to drive an arm cylinder in an “arm in” mode, and FIG. 2 is an enlarged sectional view illustrating a main part of a regeneration valve shown in FIG. 1.
As shown in FIG. 1 and FIG. 2, a control valve provided with a regeneration valve for a heavy equipment according to the related art includes a hydraulic cylinder C (arm cylinder) connected with a hydraulic pump (not shown), an arm control valve AV provided in a path between the hydraulic pump and the hydraulic cylinder, controlling operation, stop, and direction of the hydraulic cylinder by switching a spool S when an external pilot signal pressure is applied thereto, and a regeneration valve RV having a regeneration switching spool 6, switched by discharge pressure of the hydraulic pump to control hydraulic oil returning from the hydraulic cylinder to the hydraulic tank.
As shown in FIG. 2, the regeneration valve RV includes a piston 8 moving depending on the discharge pressure of the hydraulic pump, a sleeve 7 having orifices 10 and 11 that respectively communicate with a return port A and a tank port T, the regeneration switching spool 6 elastically provided in the sleeve 7 by a valve spring 5 and switched during motion of the piston 8 to control regeneration oil moving from the return port A to the tank port T, and a piston 3 provided at the end of the valve spring 5, increasing or reducing elasticity of the valve spring 5 while moving depending on an external signal.
The single operation of the actuator will now be described.
If the spool S is switched to a right side when viewed from the drawing as an external pilot signal pressure is applied to a pilot port PP of the arm control valve AV, the hydraulic oil discharged from the hydraulic pump pushes a check valve 4 in an upward direction when viewed from the drawing after passing through the pump port and is supplied to a large chamber C1 of the hydraulic cylinder C.
The hydraulic oil discharged from a small chamber C2 of the hydraulic cylinder C pushes a holding poppet in an upward direction when viewed from the drawing and passes through the spool S. The hydraulic oil is then moved to the tank port T through the orifices 10 and 11.
At the same time, the hydraulic oil of the pump port 2 moves the piston 8 and the regeneration switching spool 6 to a right side of FIG. 2 to reduce the diameter of the orifice 10. This reduces pressure loss of the hydraulic oil moving from the return port A to the tank port T.
At this time, leakage oil occurs due to a clearance generated by difference between the inner diameter of the sleeve 7 and the outer diameter of the switching spool 6. The leakage oil is moved to a piston chamber 1 and to the tank port T through a drain hole 12 of the sleeve 7. In this case, rear pressure occurs in the piston chamber 1 due to a small diameter of the drain hole 12. The rear pressure increases with the lapse of time so that the switching spool 6 may be switched to a left side when viewed from the drawing, thereby moving the piston 8 to the left side.
In other words, the condition, [(pressure of the pump port 2) (water pressure area of the piston 8)]<[(rear pressure of the piston chamber 1) (water pressure area of the switching spool 6)] is fulfilled.
Meanwhile, since the sectional area of the orifice 11 is reduced if the switching spool 6 is switched to the left side, the pressure at the return port A increases rapidly. The increasing pressure is combined with the hydraulic oil of a rear pressure chamber 15 through the regeneration check valve CV and then moves the piston 8 to the right side in the drawing.
In other words, the condition, [(pressure of the pump port 2) (water pressure area of the piston 8)]>[(rear pressure of the piston chamber 1) (water pressure area of the switching spool 6)] is fulfilled.
Repetition of the above operation causes hunting of the equipment.
The composite operation of the actuator, for example, composite driving of arm in and swing, will be described.
In a state that the switching spool 6 and the piston 8 are moved to the right side, if a pilot signal pressure of 40K is applied to the pilot port PP of the regeneration valve RV to pivot the equipment, the piston 3 is moved to the right side so that the switching spool 6 and the piston pushed to the right side may be switched to the left side.
In other words, the condition, [(pressure of the pump port 2) (water pressure area of the piston 8)]<[(40K) (water pressure area of the piston 3)] is fulfilled.
The orifices 10 and 11 are fixed without motion until a certain pressure increases. Pressure loss at the return port A increases as the sectional area of the orifice 11 is reduced by switching of the switching spool 6. For this reason, the swing operation of the hydraulic cylinder C is first performed.
If the pressure loss value increases as the flow increases, the condition, [(pressure of the pump port 2) (water pressure area of the piston 8)]>[(water pressure area of the piston 3) (40K)] is fulfilled.
At this time, the piston 3, the switching spool 6 and the piston 8 are instantaneously moved to rapidly increase the sectional area of the orifice 11, thereby reducing the pressure loss value ΔP.
If the pressure loss value is reduced, the condition, [(pressure of the pump port 2) (water pressure area of the piston 8)]<[(water pressure area of the piston 3) (40K)] is fulfilled.
Repetition of the above operation causes hunting of the equipment.
The hydraulic oil from the pump port 2 is leaked through the clearance generated between the piston 8 and the sleeve 7 and the clearance generated by difference between the inner diameter of the sleeve 7 and the outer diameter of the switching spool 6. The leakage oil is moved from a recess groove at a left side of the switching spool 6 to the piston chamber 1 through an orifice 13 of the switching spool 6.
At this time, the orifice 13 has a small diameter that fails to desirably discharge the hydraulic oil, thereby pressurizing the left side of the switching spool 6. Therefore, the hydraulic oil is moved by force of the switching spool 6 not external force caused by motion of the piston 8.
For this reason, the hydraulic pressure is relatively reduced against specifications of a hydraulic circuit, thereby deteriorating reliability.